Ch. 7 Sec. 3 Formation of Soil

Soil Essential for life on earth Growing plants for food and oxygen Homes for organisms

Development of Soil Soil development differs in each area Soil is broken down rock particles and decaying organic matter: ____________ Provides nutrients to the soil Chemical and mechanical weathering

Soil Composition Soil forms in layers Residual Soil Parent soil is the solid bedrock from which other pieces break off From Parent bedrock  weathering occurs Soil composition differs depending on location Residual Soil Soil located above it’s parent material Kentucky Blue grass soil

Soil Composition Transported Soil Soil moved away from parent bedrock due to erosion Proportions between soil and bedrock differ due to chemical weathering Highly acidic areas have lower organic materials

Soil Profiles Vertical sequence of soil layers Soil Horizon Poorly developed soils show little difference between layers Soil Horizon Three major  A, B, & C The D layer is the Rock bed

Soil Profiles A: high concentration of organic matter & humus Dark Colored B: Sub-soils that are enriched with clay materials Washed out materials from topsoil Red or brown due to iron oxides C: Above bedrock, contains weathered parent material

Topography Topography affects thickness of soil Soils on slopes are thin due to run-off Soils in lower valleys are thick Slopes facing sunlight (South in N. hemisphere) have high vegetation and thicker soils

Soil Types Polar High latitudes and high elevations Good drainage but very thin horizons: only cm’s thick Permafrost (frozen ground) under polar soils

Soil Types Temperate Soils Able to support many diverse environments Grassland  high in humus Forest  high in aluminum rich clays

Soil Types Desert Soil Receive low levels of precipitation High level of accumulated salts Little organic matter  Very thin A Horizon

Tropical Soils Tropical Soil High temps & high precipitation lead to infertile soil Very little humus but high in iron and aluminum High oxidation (red soil) Poor growth conditions

Soil Texture Soil classified accord to size Clay (smallest), silt, or sand (largest) Texture of a soil affects its capacity to retain water and its ability to support growth

Soil Fertility How well soil can support plant growth Determined by: 1) Availability of nutrients 2) Number of Microorganisms 3) Amount of precipitation Addition of limestone reduces acidity and enhance crop growth